Almost all acrobatics are based on one or more of three elements: loop, roll, and stall. Thus, these three maneuvers deserve more attention in this writing and in your practice sessions than any others. The versions presented are very simple and easy to perform, but should not be confused with more sophisticated (and much more difficult) variants discussed in Chapter 11. The best way to begin aerobatic flying in RC is to have a qualified instructor demonstrate each maneuver for you and monitor your attempts to perform the maneuvers until you have demonstrated good control during this type of maneuver. However, if you wish to attempt basic aerobatics without the aid of an instructor, the following material explains how that could be done.
Most trainers are capable of performing a loop from level flight, but will benefit from the added speed of a low angle dive. Be sure the plane is at least a couple of mistakes high before attempting this or any other “stunt” described in this chapter. Enter a low angle dive parallel to the flight line, give the plane a few seconds to build up speed (at full throttle), and pull full up elevator (many trainers will loop well with about ½ displacement of up elevator at the beginning). The trainer will go up, over to inverted, and enter a dive, hopefully describing a nice, round circle. You may find that it helps to reduce the amount of up elevator that you are holding as the airplane goes over the top of the loop. If that is the case, you will want to re-introduce up elevator during the down side of the loop. You may also find it useful to reduce throttle during the downside of the loop to keep speed from building up and to help describe a more symmetrical circle. As your plane nears horizontal flight again, ease off the elevator so that you exit the loop in smooth, horizontal flight (and return the throttle to normal cruise setting if appropriate). This is called an inside loop as the top of the airplane is to the inside of the loop. Few trainers can complete an outside loop, so that discussion is saved for Chapter 11.
Once again the trainer benefits from some added airspeed, so full throttle and a shallow dive is used as in the loop. When the speed is satisfactory pull into a slight climbing attitude, neutralize the elevator, and apply full aileron until the model approaches upright flight, then ease off the aileron so the plane exits the maneuver in horizontal flight with wings level. Do not attempt to perform multiple rolls as the airplane nose will point more and more toward mother earth unless coordinated rudder and/or elevator inputs are made—a technique that is beyond the scope of this chapter.
A stall is a condition where there is simply not enough lift being generated to support the plane’s weight. Stalls can occur at any speed and are strictly a function of lift generation and effective weight. Remember that weight of an airplane at any point can be increased beyond its static weight by loading the supporting surfaces (by rapid up elevator, for example). We will deal with low speed stalls here, but there is another condition that is a high speed stall such as used for snap rolls and other advanced maneuvers. In its simplest form reducing throttle while maintaining level flight loses speed. Because of the reduced airspeed, the airfoils (wings) of the airplane must assume increasing angles with respect to the airflow. From a flying perspective, more and more up elevator must be applied to hold level flight. At the end of this slowing process, every airplane will reach a condition in which the main supporting airfoil (main wing) cannot generate sufficient lift to support the weight of the airplane. In this situation a conventional airplane (engine in front and negative load elevator in the back) will begin to fall, usually in a more or less wings level attitude. Since the engine weight will become dominant, a nose down attitude will usually obtain after the stall. In a stable conventional airplane, the drop of the nose caused by a lack of sufficient lift will return to the aircraft to a speed sufficient to allow return to normal flight. For recovery from a stall one should allow the airspeed to build up and increase throttle to return to level, controlled flight while maintaining the same heading on which the maneuver was entered.
Turn Around Maneuvers
Student pilots are rarely introduced to turn around maneuvers because most training programs emphasize racetrack and figure eight level, climbing and gliding flight patterns. This is because basic training is intended to prepare a student for safe, well-controlled landings. However, there comes a time when turning the airplane in an normal upright attitude is no longer satisfying or appropriate and more may be needed. Most, if not all of these had their origin in wartime combat as a means of doing unto the opposition before they got to you.
Immelmann. Lieutenant Von Immelmann, flying a Fokker Eindecker during WWI came up with this one. The Eindecker used wing warping instead of ailerons and did not have much roll authority, making this a very sporty maneuver for its day. It consists of a half loop followed by a half roll to provide reversal of direction and return to upright, horizontal flight.
Perform a basic loop as described above except as the aircraft gets to the top of the loop neutralize the elevator and input full aileron. Roll the plane upright easing off the aileron as the wings approach level. Note that this is a combination of two basic maneuvers.
Split S. This might be thought of as a reverse immelman as the plane is rolled inverted and pulled through a half loop to achieve direction reversal and upright, horizontal flight.
Although not really necessary, most people enter the split S from a slight climbing attitude and this is certainly recommended for your initial attempts. Perform a half roll easing off the aileron (or rudder if no ailerons) as inverted wings level is approached, and apply up elevator. Retarding the throttle to high idle at this point is almost always a good idea. As the plane nears upright horizontal flight, ease off the elevator for a smooth exit. (and add throttle to normal cruise if appropriate) It seems that some pilots hold full throttle throughout this maneuver and the aircraft builds up a lot of speed, but throttling back before pulling up elevator at the entry will make it a bit tamer, will reduce the possibility of over-stressing the aircraft during pull out and will reduce the amount of altitude needed to safely complete the split S maneuver.
Wingover. This is executed just like the stall turn except full throttle is maintained and there should not be a stall. Indeed, the airplane is literally flown through this maneuver. From level, full throttle flight, pull to a vertical line continuing up until the speed begins to fall off, then apply full rudder toward the direction that you want to turn the plane. Hold rudder until the airplane flies around the turn easing off as the vertical down line is approached. Pull into horizontal flight at the same altitude the maneuver was initiated from and exit in the opposite direction.
More "turn around" maneuvers are explored in the full text of our book (see link below).